The UB collaboration at the LHCb experiment

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The UB collaboration at the LHCb experiment

• Introduction to LHCb
• The LHCb Calorimeters
• Participation of the UB

Ernest Aguiló Chivite IFAE, Bellaterra, 10 6
2005
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Introduction to LHCb
Will study CP Violation in the B meson system

• LHC -pp collisions _at_ 14TeV
• -Bunch crossing frequency 40 MHz
  Spill-over
• -full spectrum of B hadrons
• ( )
• -high intensity

• LHCb
• - single arm spectrometer
• - 15-300mrad angular acceptance
• - will just use
  to avoid events with multiple interactions.

p
p
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Introduction to LHCb
CP Violation is one of the keys

• Why is there no antimatter in the Univers?
• Sakharov Arguments
• Proton Desintegration
• Non equilibrium (Big Bang)
• CP violation (Cchanging particle- antiparticle,
  PParity r ? -r)

The idea is to study processes and compare them
with their CP conjugates
Indicates CP violation
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Introduction to LHCb
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Introduction to LHCb
VELO

• Vertex locator around the interaction region
• Measures impact parameter, displaced vertex
• Silicon strip detector with 30 ?m impact
  parameter resolution

Pile-up Veto 2 VELO sensors to measure the
number of primary interactions at first trigger
level
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Introduction to LHCb
Ring Imaging Cerenkov Detectors
RICH2
RICH1
Aerogel gas (C4F10)
Gas (CF4)
Two RICH detectors for charged hadron
identification Provide gt 3? ?-K separation for
3ltplt80 GeV
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Introduction to LHCb
Tracking

• Silicon
• Trigger tracker
• Inner tracker
• Straw tubes
• Outer tracker

• Tracking system and dipole magnet to measure
  angles and momenta
• ?p/p 0.4
• Magnetic field regularly reversed to reduce
  experimental systematics

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Introduction to LHCb
HCAL
ECAL
UB
SPD/PS
Calorimeter System

• To identify electrons, hadrons and neutrals
• Important for the first level of the trigger
  (L0)
• Scintillator Pad Detector
• Preshower
• Electromagnetic calorimeter
• Hadronic Calorimeter Fe
  Scintillator

Pb Scintillator
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Introduction to LHCb
Muon Chambers

• Muon identification transverse momentum
  measurement for L0
• MWPC 3-GEM (where higher particle rates)

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Introduction to LHCb

• Trigger
• Need
• The multilevel trigger chain

2 kHz
50 MB/s ? 0.5 PB/yr
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The LHCb Calorimeters
SPD/PRS/ECAL
SPD/PRS

• HCAL
• Resolution

• ECAL
• Resolution (E in GeV)
• Shashlick technology

6000 cells 3 zones
Separated by a 2.5 X0 Pb plate
Scintillator emits blue light
Inner (4x4 cm2)
scintillator
1500 cells 2 zones
iron
fibres cross the tiles
Middle (6x6 cm2)
1.5 cm
66 lead/scintillator periods
Outer (12x12 cm2)
5.6 lI
fibre loops
clear fibre PMT
entering hadrons
25 X0
fibres running parallel
Side View
Front view
WLS fibre captures it and reemits in green
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The LHCb Calorimeters
Working Principle
PRS
But a photon or an electron form a previous
bunch-crossing could leave signal in the SPD
SPD
ECAL
HCAL
e-

• Interaction
• Backsplash
• 15 signal from other bunch
• crossing

0.7 m.i.p. threshold
g
p-
Correction done at hardware level
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Participation of the UB
Hardware
Cosmic ray tests
Characterisation Tests
Design Testing
Radiation Hardness Tests
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Participation of the UB
Simulations, Physics Computing

• Backsplash Photon Interaction
• SPD/PRS Pulseshape Simulation
• Calorimeter L0 Trigger
• Bd ? J/y(ee-)KS
• Flavor Tagging studies are being made in the Bd
  ? J/y(ee-)KS channel
• GRID a farm of 30 (P4 _at_ 2.8 GHz) PCs for the
  GRID at the Physics Faculty.

Next slides
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Participation of the UB
Backsplash

• Test-beam with electrons and photons on October
  1999 to measure 180o backsplash photon
  interaction

462 GeV gs
0.7 m.i.p.
0.80.3
1.40.6
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Participation of the UB
Backsplash

• Test-beam with electrons and pions on July 2003
  to measure lateral backsplash

(EGS4)
(EGS4)
(GEANT)
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Participation of the UB
SPD/PRS Pulseshape Simulation

• Needed to introduce spill-over effects in the
  LHCb general simulation
• Fast Monte Carlo
• simulation method
• developped that
• reproduces correctly
• a full MC simulation
• and is 6000 times
• faster
• Fast MC fitted to
• cosmic ray tests data

Full MC
Fast MC
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Participation of the UB
Calorimeter L0 Trigger
SPD
PRS
ECAL
e/e-
ETgtETe (2.8 GeV)
Electrons Photons
L E A D
g
ETgtETg (2.6 GeV)
SPD Mask g or e/e-
PRS Mask 1 or 2 cells with EPRSgtEth (10 MeV)
Shower contained in a cluster (2x2 cells)
highest ET in card
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Participation of the UB
Calorimeter L0 Trigger
Electron trigger
Photon trigger
Eff.
Eff.
current
2.87 GeV ET cut improvement 20.5
2.58 GeV ET cut improvement 9.8
current
Maximum 1 PRS cell
Maximum 3 PRS cells
Maximum 2 PRS cells
Maximum 4 PRS cells
Eth (MeV)
Eth (MeV)

• Needs confirmation by studying the total L0
  efficiency
• Currently p0 L0 Trigger is being studied

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Participation of the UB
Bd ? J/y(ee-)KS reconstruction

• 0.3 radiation lenghts before the magnet ? 26
  e/e- energy radiated
• To recover bremsstrahlung
• But there is still a 25 MeV shift
• in the J/y mass peak
• Proposed solution
• Mass constrained fit
• Modify in a controled way the e/e- covariance
  matrix to allow big changes in their energy ?
  correct J/y energy

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Participation of the UB
Bd ? J/y(ee-)KS reconstruction
Pull distributions
After (f?0.7)
Before (errors underestimated)
J/y Energy m 5.692 s 6.133
B Mass m 0.5132 s 3.205
J/y Energy m 0.01198 s 0.9624
B Mass m 2.5x10-4 s 0.9991
B Energy m 3.349 s 6.779
B q m -0.2922 s 4.394
B Energy m 0.03807 s 1.013
B q m -0.02085 s 0.9838
It is still being worked on